The invention concerns arrangement of the course of the thread in a texturing machine for plied yarns. The threads and resulting yarn are usually at least partially of a plastic material, which may be extruded or spun from a mass. Such texturing machines have a plurality of units for texturing yarn. Each such unit typically requires a respective heating passage in which the thread is heated before it is textured. An increase in the number of texturing arrangements requires a corresponding increase in the number of heating passages. The heater is usually a contact heater with a respective channel defining a heating passage for each thread, and the thread is heated by contact with a wall of the channel.
U.S. Pat. No. 4,584,831 describes a device for the false twisting of threads which makes it possible for two complete texturing units to be arranged in a very narrow space on only one support. The device is particularly suitable for the conversion of existing texturing machines on which doubled yarns and particularly with a right hand or regular twist or turn (in Germany referred to as a Z-twist) and with a left hand or reverse twist or turn (in Germany referred to as an S-twist) are to be worked together. These machines are usually equipped with heaters which are designed for a particular number of fiber texturing places. For instance, if there are 192 texturing places, only 192 heating channels are present. For doubling of yarn production by use of the above-mentioned two unit false twisting arrangements, a new heater is required in the normal case in order to be able to texture the threads unimpeded.
German Utility Model No. 75 22 099 describes a thread guide which is arranged above the heater. The guide is intended to prevent the threads from contacting each other within the heater. Such contact would form closed places, so-called "tight spots." Separating the two threads only at the outlet of the heater by means of the thread guide does not prevent the threads from striking against each other within the heating channel, since neither the direction of travel of the thread nor the direction of twist of the thread is taken into account. The danger of "tight spots" and of thread breakage is still present.